Powdery developing material for electrophotographic reproduction

Abstract

A dry developing powder composition particularly suited for use in electrophotographic reproduction which comprises a magnetic toner of 35 to 50 microns in average particle size mixed with a non-magnetic toner of 5 to 30 microns in average particle size. The amount of the magnetic toner used is within the range of 85 to 98% by weight relative to the total weight of the composition and the amount of the non-magnetic toner used is within the range of 2 to 15% by weight relative to the total weight of the composition.

What is claimed is: 
     
       1. A dry developing powder composition for use in a rotating magnetic brush developing apparatus consisting essentially of (A) 85 to 98 wt% of a magnetic toner capable of functioning as a developer comprising a mixture of a styrene-acrylic resin, magnetite in a finely divided state, and a coloring agent; and (B) 2% to 15% of a non-magnetic toner comprising a mixture of a styrene-acrylic resin and a coloring agent, said percentages being based on the total weight of the composition, said magnetic toner (A) and non-magnetic toner (B) being produced by mixing together the components making up each individual mixture (A) and (B), kneading the mixture by use of a heating roll, cooling the mixture and pulverizing each of said magnetic toner mixtures (A) and non-magnetic toner (B) thus-produced so that said magnetic toner has an average particle size within the range of 35 to 50 microns and said non-magnetic toner has an average particle size within the range of 5 to 30 microns. 
     
     
       2. A dry developing powder composition as claimed in claim 1, wherein the respective amounts of the magnetic and non-magnetic toners are within the range of 90 to 95% and within the range of 5 to 10%. 
     
     
       3. A dry developing powder composition according to claim 1 wherein the magnetic toner comprises 100 parts by weight of resin, 200 parts by weight magnetite, and 8 parts by weight of coloring agent and wherein the non-magnetic toner contains 100 parts by weight of resin and 8 parts by weight of the coloring agent. 
     
     
       4. In a dry magnetic brush developing process involving the use of a brush developing apparatus of a magnetic rotating type containing a rotary magnetic unit rotatably enclosed in a developing sleeve, comprising electrostatically charging a photoconductive support medium, forming an electrostatic latent image on the photoconductive support medium in a pattern corresponding to the original image to be produced, contacting the photoconductive support medium with a dry developing powder by means of said magnetic brush in which said developing powder is moved to the counter surface of said developing sleeve by the rotation of said rotary magnetic unit so as to be in contact with said photoconductive support medium, thereby developing the electrostatic latent image into a powder image and transferring the powder image onto a final support material, the improvement wherein the dry developing powder consists essentially of (A) a magnetic toner capable of functioning as a developer comprising a resin, a finely divided magnetic material and a coloring agent, in an amount within the range of 85% to 95% and (B) a non-magnetic toner capable of being triboelectrically charged through mixing with said magnetic toner comprising a resin, a coloring agent and a dye, in an amount within the range of 2% to 15%, said percentages being based on the total weight of the powder composition, said magnetic toner (A) and non-magnetic toner (B) being produced by mixing together the components making up each individual mixture (A) and (B) kneading the mixture by use of a heating roll, cooling the mixture and pulverizing each of said magnetic toner mixture (A) and non-magnetic toner mixture (B) thus-produced so that said magnetic toner has an average particle size within the range of 35 to 50 microns and an electro-resistivity ranging from 10 5  to 10 14  Ω.cm., and wherein said non-magnetic toner has an average particle size within the range of 5 to 30 microns.